postpone evaluation of constants whose substs depend on inference vars or regions

Author: b-naber

compiler/rustc_infer/src/infer/mod.rs

@@ -21,6 +21,7 @@ use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues};
 use rustc_middle::infer::unify_key::{ConstVarValue, ConstVariableValue};
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind, ToType};
+use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::mir::interpret::EvalToConstValueResult;
 use rustc_middle::traits::select;
 use rustc_middle::ty::error::{ExpectedFound, TypeError};
@@ -1584,10 +1585,23 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         unevaluated: ty::Unevaluated<'tcx>,
         span: Option<Span>,
     ) -> EvalToConstValueResult<'tcx> {
-        let mut original_values = OriginalQueryValues::default();
-        let canonical = self.canonicalize_query((param_env, unevaluated), &mut original_values);
+        let param_env = self.tcx.erase_regions(param_env);
+        let mut substs = unevaluated.substs(self.tcx);
+        substs = self.tcx.erase_regions(substs);
+        substs = self.resolve_vars_if_possible(substs);
+
+        // Postpone the evaluation of constants whose substs depend on inference
+        // variables
+        if substs.has_infer_types_or_consts() {
+            return Err(ErrorHandled::TooGeneric);
+        }
+
+        let unevaluated = ty::Unevaluated {
+            def: unevaluated.def,
+            substs_: Some(substs),
+            promoted: unevaluated.promoted,
+        };
 
-        let (param_env, unevaluated) = canonical.value;
         // The return value is the evaluated value which doesn't contain any reference to inference
         // variables, thus we don't need to substitute back the original values.
         self.tcx.const_eval_resolve(param_env, unevaluated, span)